1. Field of the Invention
This invention relates to the areas of graphene, carbon nanotubes (CNTs), and high-conducting wires.
2. Prior Art
Graphene is a plane atomic monolayer of carbon crystal hexagonal lattice with one atom at each apex of the hexagon, and with the bond length between two neighboring atoms equal to 1.42 angstroms (see FIG. 1). Each hexagon is sometimes called a benzene ring. This atomic monolayer of carbon crystal is the basic building block of graphite which can be considered as formed by stacking up numerous layers of graphene with much weaker bonds in the direction normal to the parallel planes of the layers. Graphene is also the basic form of all graphite related molecular forms: the microscopic soccer ball-like buckyballs, other spheroid-shape molecules, and carbon nanotubes (CNTs). All these are categorized as fullerences. While all spheroid type molecules can be thought of as graphene wrapped in closed forms, carbon nanotubes (single-walled nanotubes (SWNTs) and multi-walled nanotubes (MWNTs)) are microscopic single-layer and multi-layer graphene rolls with open ends and with their circumferences just a few benzene rings across.
The existence of graphene was discovered in 2004 (Ref. 1) and the stability of this material was confirmed in 2007 (Ref. 2). Since its discovery, graphene, due to its peculiar physical properties, has become the hottest chased-after material in the scientific community around the world (Ref. 3). On the other hand, the discovery of CNTs can be traced back to over half a century when L. V. Radushkevich et al. reported finding on these materials in the Soviet Journal of Physical Chemistry in 1952. Carbon nanotubes have been produced and reported since then. But it was not until the 1990's that the importance of CNTs began to catch people's attention.
Researches on graphene, CNTs, etc. have shown enormous potential applications of these materials (due to their high electron mobility and mechanical strength, extreme hardness, flexibility, etc.) in the electronic, electrical, mechanical, medical, environmental, composite materials, and energy production, transport, and storage industries, besides their fundamental research values (Refs. 3, 4, 5, 6). However, the limited production capacity of these materials, both in quantity and unit (molecule) size, have so far prevented realization of these potentials to reach industry levels. Current graphene and CNT production methods are described as follows.
On graphene production, a few known methods are (Refs. 3, 4, 7): mechanical exfoliation, works by searching for microscopically small pieces of graphene from graphite abrasion debris under an optical microscope; Ultrasonic exfoliation, by drying out sheets of graphene powder, generated from ultrasound break-up graphite target, spreading on water surface; chemical exfoliation, by drying out graphite dissolving organic solutions (can have graphene sizes up to few tens of square microns); chemical vapor deposition (CVD), by flowing a hydrocarbon gas over a heated surface, causing carbon atoms decomposed from the gas to form graphene on downstream cooler surfaces (can have graphene sample sizes up to a few square centimeters). All these methods are having quality problems.
Owing to a much longer period of development, CNT manufacturing technologies are more productive than those of graphene's, and the currently available methods include: CVD method (Ref. 8), works by flowing a carbon-containing gas over a heated surface with a distribution of metal nanoparticles to act as a catalyst to produce CNTs (both SWNTs and MWNTs); arc discharge (Ref. 9), both SWNTs and MWNTs are produced on graphite electrodes in an arc discharge; laser ablation (Ref. 10), by laser ablation of a graphite target in a high temperature reactor. As in the cases of graphene manufacturing, all these methods have quality problems.